It is frequently desired to form high quality layers of material over semiconductor substrates during semiconductor device fabrication. Among the materials which can be included in such layers are tantalum pentoxide, titanium nitride, titanium silicon nitride, tantalum nitride, tantalum silicon nitride, titanium silicide, tantalum silicide, tungsten nitride, aluminum oxide, hafnium oxide, zirconium oxide, silicon nitride, silicon dioxide, elemental tungsten and elemental titanium. Numerous methods have been developed for forming layers of such materials, with exemplary methods including chemical vapor deposition (CVD), and in some cases atomic layer deposition (ALD).
Chemical vapor deposition comprises mixing two or more reactants in a chamber to form a material which subsequently deposits across exposed surfaces of one or more semiconductor substrates. An advantage of chemical vapor deposition is that it can be utilized in batch processes, or, in other words, can be utilized to simultaneously treat a plurality of discrete semiconductor substrates. Among the disadvantages of chemical vapor deposition is that it can be difficult to control reactions between the reactants provided in a chamber, and accordingly various side-reactions can occur to generate contaminants. Additionally, it can be difficult to form a uniform layer over multiple exposed surfaces of one or more semiconductor substrates with CVD. The deposition of CVD material can be faster in various regions of semiconductor typography than other regions, leading to non-uniformity in a thickness of the deposited material across various exposed surfaces of semiconductor substrates provided within a CVD reaction chamber.
ALD can overcome some of the problems discussed above relative to CVD. ALD processing typically comprises forming thin films of material by repeatedly depositing monoatomic layers. The technique involves individually depositing precursors, or reactants, that react in situ to form a desired film of material across a semiconductor substrate. More specifically, ALD processes involve introduction of a first reactant which reacts with a substrate to form a monolayer across the substrate. The first reactant will typically react with the substrate, but not with itself. Accordingly, side-reactions are eliminated. Further, the reaction of the reactant with the substrate is self-limiting, in that once a monolayer forms across exposed surfaces of the substrate there is no longer further reaction of the reactant with the substrate.
After the monolayer is formed, the first reactant is flushed from the processing chamber, and a second reactant is subsequently introduced. The second reactant reacts with the monolayer of material formed from the first reactant to convert such monolayer into a desired mass over the substrate. The desired mass can be uniformly thick across the various surfaces of the substrate. The mass can be made thicker by repeating the above-described process. Specifically, the mass can become an upper surface of a semiconductor substrate, and can be utilized for reaction with the first reactant. Subsequently, the second reactant can be introduced to form a second layer of the mass over the first layer. The process can be repeated until a desired thickness of the mass is formed.
A problem with existing ALD technologies is that such are not typically suitable for utilization in batch processes. Rather, semiconductor substrates are treated one at a time, and throughput of substrates through ALD processes is thus low relative to CVD processes. Some effort has recently been made to develop batch processes for ALD of silicon nitride. Specifically, a batch of wafers is exposed to trichlorosilane in a reaction chamber to form a silicon-containing monolayer over exposed surfaces of the substrates. Subsequently, the trichlorosilane is evacuated from the chamber and ammonia is introduced to convert the silicon-containing material to silicon nitride. The trichlorosilane deposition occurs at a temperature at least 150° C. different than the ammonia treatment.
It would desirable to extend batch ALD processes to other materials besides silicon nitride. It would also be desirable to develop improved processes for batch ALD of silicon nitride.